This is a little like an old school margarita but with vodka in lieu of tequila. The proportions would probably work well with gin or tequila as well.
3 oz vodka
1.5 oz fresh squeezed grapefruit juice
.5 oz fresh squeezed lime juice
1 tspn kosher salt (too taste)
Combine all ingredients in a shaker, fill to 1/3 to 1/2 with ice and shake vigorously. Strain into low ball or martini glass, taste and adjust salt to taste.